Reference signals, for example the test lines in a television image, can be utilized to measure the signal-to-noise ratio of, for example, a digitized television image. This procedure requires, however, a complex and expensive test receiver with corresponding measurement technology. The monitoring of pilot signals requires a similar outlay.
A method for determining the quantization distortion of transmission devices is described in European Patent Application No. 0 030 383, where a certain frequency band is provided at the transmitter end and fed into a transmission device. At the receiver end, a level measurement is performed within a transmitter-end frequency band, along with a measurement outside that frequency band. The quantization noise ratio is determined from a difference between these two measurements.
A method for determining signal power and distortion power is described in European Patent Application No. 0 069 972. Two signals are generated; the first digital signal is transmitted directly to a receiver end; the second signal is initially conveyed to a codec. The distortion power is determined from samples of the received signals. German Patent Application No. 29 45 034 describes an arrangement for measuring a ratio of a signal distortion to a quantization distortion. Two level meters are used to determine the difference between a reference signal and a noise signal containing the quantization distortion.